In production plants of the synthetic fiber industry, waste products such as polymer lumps, cables, entangled masses of filaments, first-spun material, undrawn and drawn fibers and filaments partly treated with finishes, rejected bobbins, etc. are accumulating in considerable quantities in the various process stages. These waste products, on the one hand, are too valuable to throw away while, on the other hand, their disposal is costly and could result in intolerable environmental pollution. Hence, the reclamation of such wastes is deemed an absolute necessity. Where the production of films from plastics is involved, the accumulating wastes suitable for reclamation amount to considerable quantities.
In principle, there exist two processes for the reclamation of polymer wastes: (1) the controlled degradation of the polymer for the purpose of recovering the monomeric starting materials, for example, the so-called depolymerization of poly - .epsilon. - caprolactam to .epsilon. - caprolactam, or the glycolysis of polyethylene terephthalate, and (2) the remelting with subsequent filtration, forming and solidification of the obtained polymer melt. Due to the large number of different high-polymers to be recovered, for example, polyamides, polyesters, polyolefins, a variety of degradation processes is required which, partly due to their complexity, involve high capital investments and maintenance costs and frequently operate with only modest yields of recoverable valuable materials.
Also the remelting processes are, in essence, designed specifically for one type of polymer and/or structure and are, thus, generally not applicable to the other types of plastics and forms of waste materials.
Particular difficulties result because the bulk weight of the polymer wastes on completion of the required cutting operation amounts to only approx. 0.1 - 0.15 kg/l. The chopped waste resembles feathers in structure which renders its continuous conveyance to the melting unit, i.e. screw-type extruder, rather problematic. In the case of remelting fibers and filaments coated with spin-finish deposits, the lubricants must first be removed by employing expensive washing and drying processes.
In the literature concerning the reclamation of wastes from synthetic fibers and foils (Maschinenmarkt MM Industriejournal, Wurzburg, 78 (1972) 4 page 65 and 66) it is pointed out that these wastes, after having been cut in a cutting mill, are of a very low bulk density so that the material moves into the extruder screws in an irregular fashion. The literature also states that stuffing screws should be provided at the extruder inlet as the cut pieces or chips tend to bridge at the silo discharge and cause disturbances in the dosing system. In the cited literature, this mode of operation is deemed to be so troublesome that it is suggested to convert the waste material into free flowing granules. This is done by passing the cut synthetic material via a dosing screw to a compacting device whose rotor seizes the chips which are then sintered under the heat of friction and pressure against a stationary counter pan. Chips that still remain in the sintered material must be separated later. The finished granules will then be available for remelting in screw-type extruders.
Due to the heat of friction required for sintering and the later remelting operation, thermoplastic materials are frequently thermally damaged so that they can no longer be processed to finished products of high quality. Neither does blending the reclaimed materials, agglomerated by compression and sintering with fresh granulate, offer a remedy. Because of the effect of frequent separation due to the different geometric configuration and size of grains the melt discharged from the extruder is of fluctuating quality.